1. Field of the Invention
The present invention relates to a method of hardening gelatin and/or a gelatin derivative with an improved hardening agent, more particularly, it relates to a method of hardening a hydrophilic colloid layer containing gelatin and/or a gelatin derivative of a silver halide photographic light-sensitive material and to the silver halide photographic light-sensitive material.
2. Description of the Prior Art
Gelatin is used as a binder for many photographic light-sensitive materials. For example, gelatin is used as the main component of a silver halide light-sensitive emulsion layer, an emulsion protective layer, a filter layer, an intermediate layer, an antihalation layer, a backing layer, a film support subbing layer and a baryta layer.
These photographic materials containing gelatin are treated with various aqueous solutions having different pH's and temperatures. Since a layer containing gelatin which has not been treated with a hardening agent has properties mainly dependent on the gelatin, it has poor water resistance and swells excessively in an aqueous solution, so that the mechanical strength is greatly reduced, and, in an extreme case, the gelatin layer is sometimes dissolved, particularly in an aqueous solution having a high temperature of above 30.degree. C. or a highly alkaline aqueous solution. These properties are fatal defects for the physical properties of layers which make up photographic light-sensitive materials.
Many compounds are known to be effective for increasing the water resistance, heat resistance and abrasion resistance of a gelatin layer by hardening.
These compounds are well known as hardeners which are used in the production of photographic light-sensitive materials. Examples of known hardeners are formaldehyde, glutaraldehyde and like aldehyde type compounds; compounds having a reactive halogen as described in U.S. Pat. No. 3,288,775 and so on; compounds containing a reactive ethylenically unsaturated bond as described in U.S. Pat. No. 3,635,718 and so on; aziridine type compounds as described in U.S. Pat. No. 3,017,280, etc.; epoxy compounds as described in U.S. Pat. No. 3,091,537, etc.; and halocarboxyaldehydes such as mucochloric acid, dioxanes such as dihydroxydioxane and dichlorodioxane, or inorganic hardeners such as chromium alum and zirconium sulfate and the like.
However, these known gelatin hardeners have one or more deffects, when they are used in photographic light-sensitive materials, in that the hardening effect is insufficient, in that the gelatin hardening rate is not sufficiently fast, so that the hardening proceeds slowly with the passage of time after the production of the photographic materials (i.e., after-hardening), in that harmful effects to the properties of the photographic light-sensitive materials occur (particularly, increase of fog, decrease of sensitivity, etc.), in that the hardening effect is destroyed by other photographic additives which are present, in that they adversely affect other photographic additives (for example, color forming couplers for color photographic light-sensitive materials), in that the preparation thereof is difficult and large scale production is not appropriate, in that the hardeners per se are unstable and storage thereof is difficult, in that they have a very strong odor which causes a decrease in work efficiency during production thereof, in that they are harmful to the human body, and the like.
It is also known that hardeners having active vinyl sulfone groups are relatively advantageous for hardening purposes. For example, divinylsulfone, which is an example of a hardener, is not practically used due to its quite harmful affects on the human body. Compounds having vinylsulfonyl groups in which such a defect is decreased are described in German Pat. No. 1,100,942, U.S. Pat. No. 3,490,911, etc.
Those vinylsulfone type hardeners have advantages as hardeners because they have generally a high hardening rate and a small after-hardening effect which is a variation of hardening effect with the passage of time, because they have less harmful effects on photographic properties such as fog formation, desensitization, etc., and because they have relatively less adverse affects on color photographic emulsions such as decoloration, etc.
However, these vinylsulfone compounds are expensive or a special method is required for their production in which a large amount of organic solvents is used in order to utilize these compounds and thus it cannot always be said that they are sufficient for practical use.
For example, since the compounds described in German Pat. No. 1,622,260 have poor water solubility, when they are used for the production of photographic light-sensitive materials, they tend to deposit in a gelatin solution nd cause difficulties during coating and an uneven hardening of the photographic layer. Further, it is essential to use a large amount of an organic solvent which involves risks of fire and explosion and is undesirable in view of the harmful effects on the human body.
The compounds described in U.S. Pat. No. 3,642,486 are improved in this point. That is, these compounds have a good solubility due to ether bonds present in the compounds and are advantageous in the production of photographic light-sensitive materials. However, a compound which is known to induce cancer is used as a starting material in the production of the compounds described in U.S. Pat. No. 3,642,486 and, thus, the production of these compounds involves a large risk.Further, mass production is also disadvantgeous, since these compounds are relatively hard to crystallize because of the presence of ether bonds. Furthermore, gelatin layers or photographic light-sensitive materials hardened with these compounds have poor resistance to dissolution in an aqueous alkaline solution and this is quite a defect when it is considered that developer solutions for photographic light-sensitive materials are most generally highly alkaline aqueous solutions.
The compounds described in Japanese patent application (OPI) No. 44164/1976 have improved solubility in an alkaline solution. However, these compounds have very poor water solubility and require the use of a large amount of organic solvent in the production of photographic light-sensitive materials which is extremely disadvantageous in view of minimizing the hazards of explosion, providing safe working conditions and preventing environmental pollution.
The compounds described in Japanese patent application (OPI) Nos. 74832/1973 and 24435/1974 have improved water solubility and reduced toxicity due to the function of a polar group introduced into their molecules, that is, an acylamide bond. However, the compounds described in Japanese patent application (OPI) No. 74832/1973 require use of acylamide which is highly poisonous to produce. Also, the compounds described in Japanese patent application (OPI) No. 24435/1974 require the use of 1,3,5-triacyloylhexahydro-s-triazine which has a relatively high cost of production and, further, they are only soluble in water substantially up to about 2 weight % at room temperature (about 25.degree. C.). In addition, the melting points and solubilities of the compounds described in Japanese patent application (OPI) No. 24435/1974 are interrelated and compounds having a higher purity have higher melting points and lower solubilities than those described in Japanese patent application (OPI) No. 24435/1974.